NATURAL PHILOSOPHY. 177 



The spiral portion of the tube contains alcohol (or any other liquid or gas), 

 while the prolonged branch contains a plug of mercury, which is in contact, 

 at its inner surface, with the alcohol, while on its other side it has a partial 

 vacuum formed in the outer end of the tube. Of course, as the alcohol 

 expands or contracts, the mercmy is moved farther from, or nearer to, the 

 axis, and the change in the position of the centre of gravity of the system 

 causes a rotation around the axis, and this motion is transferred by levers 

 to a needle-point, which is lifted or depressed, according as the alcohol is 

 expanded or contracted. In front of the needle, a band of paper is made to 

 pass with an uniform motion, communicated to it by rollers, which at the 

 same time print upon it a series of horizontal and vertical lines, the former 

 of which correspond to certain temperatures, and the latter record the hours. 

 And, by a modification of its striking works, the same clock-work which 

 governs the motion of these rollers, causes a vertical bar to press, at the end 

 of every five minutes, the needle-point through the paper, from which it is 

 immediately withdrawn by a spring, thus impressing a permanent and 

 easily visible mark, recording the temperature of the instrument at that 

 instant of time. 



As regards the practical value of this invention, a committee of the Frank- 

 lin Institute, Philadelphia, have reported as follows : 



1st. The power developed by the instrument is considerable. The mechan- 

 ical force exerted by the displacement of a mass of mercury with a consid- 

 erable leverage from the centre of motion, is so great as to insure the 

 satisfactory operation of the instrument, and to allow of considerable resist- 

 ance at its working parts, without deranging its action. 



2d. This instrument is invariable; being once graduated and set, very 

 ordinary care is sufficient to prevent any derangement of its mechanism ; its 

 record will, therefore, probably remain the same, without derangement of its 

 zero, or change in the length of its degree. 



3d. It is, considering its utility, not too expensive. The inventor estimates 

 that a perfect instrument can be made for twenty to fifty dollars. This in- 

 cludes, of course, no estimate for ornamentation. For a meteorological 

 observatory, or for the ordinary recording of atmospheric temperatures at 

 home, this is not an extravagant expense. And it does not appear that any 

 more repairs ought to be required for an apparatus of this kind, than for the 

 common clock, which forms its basis. 



It is, however, only for recording atmospheric temperatures, and for ob- 

 servatories or houses, that the apparatus is fitted. It occupies considerable 

 space, and from its structure could not be conveniently carried in travelling, 

 except by sea. As, however, the scale and the motion of the paper may be 

 varied at pleasure within extensive limits, it appears possible to arrange the 

 apparatus either for very delicate registering during a comparatively short 

 time, or for a long-continued course. If the clock could be kept in motion, 

 as is now quite possible, there is no reason why the apparatus might not be 

 left to itself, to record the temperatures during a whole year, during which 

 time it would require neither superintendence nor adjustment. 



Mr. Hall, moreover, proposes modifications in the form of the instrument, 

 by means of which it may be made to record within an apartment the tem- 

 perature of the air outside, indicating the actual temperature at every instant, 

 while it records them as usual every five minutes. Journal Frank. Inst., 

 June 18-39. 



